(Sharecast News) - Four major high street banks - HSBC, Lloyds, TSB, and Allied Irish Banks (AIB) - have been found in violation of rules set by the Competition and Markets Authority (CMA), it emerged on Thursday.

The regulator said the breaches pertained to the Retail Banking Market Investigation Order 2017, which mandates transparency and accuracy in customer information.

It said HSBC failed to update information about its branches, listing 167 closed branches as open and omitting two operational branches.

Additionally, the bank did not accurately display annual rates for business loans and overdrafts on its website and misinformed some customers about unarranged overdraft charges on their personal current accounts.

TSB, owned by the Madrid-listed Banco de Sabadell, similarly did not disclose the correct maximum charges for unarranged overdrafts on personal current accounts.

The Dublin-listed AIB was meanwhile found to have incorrect annual rates for certain loans and overdrafts, both through Open Banking and its website, while Lloyds failed to list 363 ATM addresses through Open Banking.

The CMA said it monitors compliance closely, and requires banks to report non-compliance within 14 days.

Lloyds, TSB, and AIB confirmed they were implementing changes, including enhancing internal procedures, improving oversight, updating checklists, and retraining staff.

HSBC, which the regulator said had more extensive breaches, had been given detailed directions by the CMA, including an action plan to ensure future compliance.

The CMA said the Retail Banking Market Investigation Order was designed to foster transparency and competition in the banking sector, benefiting consumers through initiatives like Open Banking, which facilitates secure data sharing and improved service innovation.

HSBC was directed to make significant changes to prevent future breaches, and all four banks had received public letters from the CMA outlining the required corrective actions.

"People deserve banks they can trust to serve them well," said CMA senior director Dan Turnbull.

"Having correct information is essential when making important decisions about our finances.

"Banks handling our hard-earned money should have adequate processes in place to ensure this happens."

Turnbull said it was "disappointing" that seven years on, the regulator had to impose formal enforcement measures to secure better compliance from a major bank like HSBC was "yet again" in breach of the rules.

"The CMA will continue to closely monitor all banks' compliance to ensure customers can clearly and confidently manage their finances."

At 1209 BST, shares in HSBC Holdings were down -1.4% at 653.7p, while those in Lloyds Banking Group were off 0.44% at 59.4p.

Reporting by Josh White for Sharecast.com.